The investigations came in the wake of media stories from last year about the £1.86m bonus paid to Mike Betts, chief executive of Motability Operations, the charity’s connected company, in addition to his £1.7m salary.

The charity was also heavily criticised for its high levels of reserves, which were £2.62bn as of March 2018.

MPs from the two committees have today criticised Motability for redacting evidence to the committee on the financial management of and the state aid received by the disability car scheme.

The MPs said that the response to the committee from the charity’s chair, Lord Sterling of Plaistow, "openly attempts to discredit the NAO’s valuation of tax reliefs benefiting the scheme, despite the charity governors and Motability Operations having agreed them before publication".

The committees suggested that Motability was not taking the NAO or the committees’ investigations seriously and had failed to disclose details of the charity’s internal review.

Frank Field, chair of the Work and Pensions Committee, said: "We are clear, the NAO is clear, the government is clear: Motability must step up, now, and demonstrate the transparency and accountability befitting an organisation that enjoys huge amounts of taxpayer’s support.

"Stop making excuses, start channelling all your vast resources into what Motability does best: giving freedom and mobility to so many disabled people."

Nicky Morgan, chair of the Treasury Committee, said: "Sunlight is the best disinfectant. So it’s extremely disappointing that Motability is refusing to provide our committees with the evidence that we have requested.

"We will continue to push for full disclosure to ensure that disabled people are provided with the best possible support."

A statement from Motability said that the charity wrote to the two select committees on Monday to set out the progress it has made on implementing the NAO's recommendations.

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